1. Field of the Invention
The invention relates to a wheel bearing device and a manufacturing method therefor.
2. Description of the Related Art
There is a wheel bearing device that includes a flanged shaft member (which may also be called hub wheel). The flanged shaft member has a shaft portion, a fitting shaft portion and a plurality of flange portions. A rolling bearing is assembled to the shaft portion. The fitting shaft portion is formed on one end of the shaft portion, and has a larger diameter than that of the shaft portion. A center hole of a wheel is fitted onto the fitting shaft portion. The plurality of flange portions extend radially outward on an outer peripheral surface located between the shaft portion and the fitting shaft portion. Each of the plurality of flange portions has a through bolt hole in which a hub bolt for fastening the wheel is arranged.
The thus configured wheel bearing device is, for example, described in Japanese Patent Application Publication No. 2003-25803 (JP-A-2003-25803).
In this wheel bearing device, a flanged shaft member (hub wheel) is shaped by cold forging using a cylindrical tube as a base material, and a plurality of circumferential portions of one shaft end portion of the cold-forged base material are cut and raised radially outward. Thus, a plurality of flange portions (raised pieces) are formed. Then, a fitting shaft portion (to which a wheel is fitted to be positioned) formed of a plurality of tongue pieces is provided at the one shaft end portion of the base material. The plurality of tongue pieces extending in the axial direction are left between the plurality of flange portions.
Incidentally, in the existing wheel bearing device described in JP-A-2003-25803, a flanged shaft member is configured so that the plurality of flange portions formed of raised pieces are formed at the one shaft end portion of a forging shaped by cold forging using a cylindrical tube as a base material.
By so doing, it is possible to reduce the weight of the wheel bearing device (mainly, the flanged shaft member).
However, in the existing wheel bearing device, after a forging is manufactured by cold forging, a plurality of flange portions formed of raised pieces need to be formed at one shaft end portion of the forging, so manufacturing costs increase.